<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  * {
    margin: 0px;
    border: 0px;
  }

  .box {
    height: 500px;
    display: flex;
    flex-direction: row;

  }

  .box .left {
    width: 200px;
    background-color: aqua;
  }

  .box .center {
    flex-grow: 1;
    background-color: blue;
    margin-left: 5px;
    margin-right: 5px;
  }

  .box .right {
    width: 100px;
    background-color: brown;
  }
</style>

<body>
  <div class="box">
    <div class="left"></div>
    <div class="center"></div>
    <div class="right"></div>
  </div>
</body>

</html>